It is known to provide an apparatus for the planing of coal, for example, from a seal thereof, utilizing a system in which the coal-planing tools and/or the tools for flights for conveying the excavated material are displaceable along an excavating trough and a conveyor trough. The chain can have respective stretches extending along these troughs.
For example, the conveyor trough may have a horizontal bottom and can be formed with channels on opposite sides of the bottom in which the tool is guided as it is entrained by the chain along this trough. The chain then passes around a direction-change device or wheel at an end of the trough to ride along the excavating trough which is disposed ahead of the conveyor trough in the direction of displacement of the machine toward the coal seam and the face to be mined. The excavating trough also may have channels in which the tool is guided. The excavating trough, moreover, may be mounted so that it can pivot about a horizontal axis relative to the conveyor trough. At the end of the excavating trough, the chain passes around another direction-change device or wheel to return to the conveyor trough.
In operation, the tools plane the coal from the seam and cast the excavated coal into the conveyor trough which carries the excavated material away. The tools then serve as conveyor flights.
In some cases, although not in all, it may be advantageous to provide additional tools which function only as chain conveyor flights and are not provided with planing surfaces or cutters capable of excavating material from the seam face.
At the direction-change devices, the tools must not only be transferred from one trough to the other during a direction change of the chain, but it is necessary to swing the horizontal tools into a substantially upright position as they move onto the excavating trough or from an upright position at the end of the excavating trough into a recumbent position for travel along the conveyor trough.
In the system of German patent document DE 35 45 302 of this type, the tools are functionally rigid and act as one piece units. This applies whether the tool is an excavating tool or only a conveyor flight.
I have found that this type of tool causes problems at the direction-change devices which can only be overcome by terminating the guides for the tool before the tool reaches the direction-change device. As a result, the travel of the tool in the region of the direction-change device becomes unguided and indefinite and there is a danger that the tool and chain will become liberated from the direction-change device and cause breakdown of the apparatus.